Not all parallelograms are rectangles. A parallelogram is only a rectangle if it has four right angles and two pairs of parallel, congruent sides. Rectangles can also be called equiangular quadrilaterals, which means that they have four sides and equal angles. If three-dimensional, a rectangle is called a parallelepiped.
Types of parallelograms that are not rectangles include rhombuses and rhomboids. A square, technically a type of rectangle, is also a parallelogram. All parallelograms have two sets of parallel and congruent sides and four edges or vertices. Parallelograms are always simple quadrilaterals, or four-sided figures, that do not intersect themselves. Finally, they always have opposite angles that are equal in measure.